W-Lan amplifier brings what?

I own a Fritzbox, the big (7590)

This one is at the bottom and I'm playing the Xbox at the top. (3rd floor)

It is clear that the internet is bad.

But I had a TP link. Down in the socket and with LAN cable connected to the router and top only into the socket.

That helped only little.

Is there a better alternative?

(NO I Can't GO TO THE ROUTER)

QUOTE: "Is there a better alternative?"

YES - are you looking here: https://www.devolo.de/

Do you have a connection on the third floor? Then it could be used at the top and bottom. The waves that the router sends out are thrown down, that's why.